CD74ACT161E.A中文资料德州仪器数据手册PDF规格书

Inputs Are TTL-Voltage Compatible

Internal Look-Ahead for Fast Counting

Carry Output for n-Bit Cascading

Synchronous Counting

Synchronously Programmable

SCR-Latchup-Resistant CMOS Process and

Circuit Design

Exceeds 2-kV ESD Protection per

MIL-STD-883, Method 3015

description/ordering information

The ’ACT161 devices are 4-bit binary counters. These synchronous, presettable counters feature an internal

carry look-ahead for application in high-speed counting designs. Synchronous operation is provided by having

all flip-flops clocked simultaneously so that the outputs change coincident with each other when so instructed

by the count-enable (ENP, ENT) inputs and internal gating. This mode of operation eliminates the output

counting spikes that normally are associated with synchronous (ripple-clock) counters. A buffered clock (CLK)

input triggers the four flip-flops on the rising (positive-going) edge of the clock waveform.

These devices are fully programmable; that is, they can be preset to any number between 0 and 9 or 15.

Presetting is synchronous; therefore, setting up a low level at the load input disables the counter and causes

the outputs to agree with the setup data after the next clock pulse, regardless of the levels of the enable inputs.

The clear function is asynchronous. A low level at the clear (CLR) input sets all four of the flip-flop outputs low,

regardless of the levels of the CLK, load (LOAD), or enable inputs.

The carry look-ahead circuitry provides for cascading counters for n-bit synchronous applications without

additional gating. Instrumental in accomplishing this function are ENP, ENT, and a ripple-carry output (RCO).

Both ENP and ENT must be high to count, and ENT is fed forward to enable RCO. Enabling RCO produces a

high-level pulse while the count is maximum (9 or 15, with QA high). This high-level overflow ripple-carry pulse

can be used to enable successive cascaded stages. Transitions at ENP or ENT are allowed, regardless of the

level of CLK.

The counters feature a fully independent clock circuit. Changes at control inputs (ENP, ENT, or LOAD) that

modify the operating mode have no effect on the contents of the counter until clocking occurs. The function of

the counter (whether enabled, disabled, loading, or counting) is dictated solely by the conditions meeting the

stable setup and hold times.